High voltage spark generator from low voltage supply

ABSTRACT

The primary winding of a high turns ratio spark transformer is connected in the anode circuit of a silicon controlled rectifier for energization from a 24 volt, 60 cycle alternating power source. A biasing resistor and blocking diode are connected in series between the anode and gate of the rectifier, while a firing capacitor is connected between its gate and cathode. Charging the capacitor fires the rectifier, causing a surge of current in the primary winding of the transformer, which surge induces a voltage in the secondary winding of insufficient magnitude to arc across the spark gap. However, as the flux field collapses, a spike of from 150 to 200 volts is induced in the primary winding. Due to the high ratio of transformation (approximately 1 to 90), this spike induces 13,500 to 18,000 volts in the secondary winding, which voltage arcs across the spark gap. The voltage spike induced in the primary drives the anode of the rectifier negative, causing it to cease conducting. This firing sequence is repeated to produce at the spark gap 7 output pulses of 180 microseconds peak duration each for each positive half cycle of the applied power.

D United States Patent 13,576,467

[72] Inventor Sharad K. Gupte 3,377,125 4/1968 Zielinski 315/209X Milwaukee, Wis. 3,213,320 /1965 Worrell 315/209 [21 1 2 1967 Primary Examiner-Roy Lake gf 1971 Assistant ExaminerE. R. LaRoche [73] Assignee Penn Controls, Inc. Attorney Arnold De Angehs Oak Brook, Ill.

ABSTRACT: The primary winding of a high turns ratio spark [54] HIGH VOLTAGE SPARK GENERATOR FROM transformer is connected in the anode circuit of a silicon con- Low VOLTAGE SUPPLY trolled rectifier for energ zation from a 24 volt, cycle alter- 2 Claims 2 Drawing FigS nating power source. A biasing resistor and blocking diode are connected in series between the anode and gate of the rectifi- [52] US. Cl 315/206, er, while a fi i capacitor i connected between i gate and 307/252, 315/208 315/254' 328/28 331/150 cathode. Charging the capacitor fires the rectifier, causing a [51] Int. Cl HHDSI) 41/23, surge of current in the primary winding of the transformer H03k 17/72 which surge induces a voltage in the secondary winding of in- [50] Field of Search 315/56, 57, ffi i t magnitude to are across the Spark gap However, as 206, 240, 254; the flux field collapses, a spike of from to 200 volts is in- 307/106, 108, 246, 252, 305; 331/1 12, 150, 151; duced in the primary winding. Due to the high ratio of trans- 328/13, 28 formation (approximately 1 to 90), this spike induces 13,500 to 18,000 volts in the secondary winding, which voltage arcs [56] References Cited across the spark gap. The voltage spike induced in the primary UNYTED STATES PATENTS drives the anode of the rectifier negative, causing it to cease 3,259,797 7/1966 Heine et al 315/174 conducting. This firing sequence is repeated to produce at the 3,309,567 3/1967 Flieder et al 315/176 spark gap 7 output pulses of 180 microseconds peak duration 3,367,314 2/1968 Hirosawa et al. 307/246X each for each positive half cycle of the applied power.

ms Li g PR SEC 4%:

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SCR R film -LO7 MS SHARAD KESHAV GUPTE INVENTOR- AT TORNE Y.

HIGH VGLTAGESPARR GENERATGR lFRGM LOW VGLTAGE SUPPLY The invention involves spark generating means and particularly such means for generating a high voltage spark for igniting fuels.

Modern day heating systems using gaseous fuels are nor mally controlled by thermostats operating at 24 volts. In such systems in order to obtain the high voltage spark necessary for igniting the gaseous fuel it is often necessary to provide a step-up high voltage transformer. The high ratio of transformation and quantity of dielectric required to produce a high voltage spark from the low voltage supply dictates a size of the spark generator package which is often prohibitive.

it is, therefore, an object of the invention to provide a high voltage spark generator operable from a low voltage supply which generator is relatively small and is economical to manufacture and maintain.

The invention involves providing a silicon controlled rectifier switching circuit in which transient voltages generated through fast switching of the silicon controlled rectifier are stepped-up" by a spark transformer to induce a voltage in the rectifier circuit of opposite polarity to the supply voltages and of sufficient magnitude to make the rectifier momentarily cease conducting. These induced transient pulses are between 150 to 200 volts peak to peak value and, in turn, induce in the secondary winding of the spark transformer several high voltage spikes of from 13,500 to 18,000 volts. With the subject arrangement, the most inexpensive silicon controlled rectifier may be utilized to provide the switching action. The rectifier is not damaged, although the currents and voltages through it momentarily far exceed its rating. This is so, since the transient pulses exist for a very short duration, while the rectifier remains nonconducting for a relatively long recovery time.

- Features and advantages of the invention may be seen from the above, from the following description of the preferred embodiment when considered in conjunction with the drawing and from the appended claims.

' In the drawing:

FIG. 1 is a simplified schematic wiring diagram of high voltage spark generator means embodying the invention; and

FIG. 2 is a diagrammatic representation of oscillograms of the voltage waveform VP appearing across primary winding PR of the transformer TRS of the FIG. 1 circuit, of the waveform AV of the low voltage supply appearing over lines L1 and L2 and of the waveform PC of the current flowing through primary winding PR of transformer TRS.

Low voltage alternating power of 24 volts at 60 cycles from any convenient source is applied to the circuitry of FIG. 1 over supply lines L1, L2. Spark transformer, generally designated TRS, comprises a primary winding PR and a secondary winding SEC. A spark gap is provided by two spaced-apart electrodes, generally designated SG, connected across secondary winding SEC. Primary winding PR is connected at one side to supply line L1 and on the other side to the anode electrode of a silicon controlled rectifier SCR of the CMMF type. The cathode electrode of the silicon controlled rectifier is connected directly to supply line L2. Afiring capacitor C of approximately 0.1 microfarads is connected between the gate and cathodes electrodes of rectifier SCR. A blocking diode D of the A13Al type and a .biasing resistor R are connected in series between the anode and gate electrodes of rectifier SCR. Biasing resistor R is selected of from 100 kilohms to 150 kilohms depending upon the characteristics of rectifier SCR, the resistor value being adjusted to provide a maximum anode current of approximately 250 milliamperes.

in one tested embodiment, transformer TRS was constructed of 175 turns of number 34 wire for primary winding PR and 16,000 turns of number 412 wire for secondary winding SEC, providing step-up" transformation of l to 90.

In operation, assume that power is supplied to the circuit of FIG. 11, as is indicated in FIG. 2 by the voltage waveform designated AV. During the start of the positive half cycle of applied voltage AV, when supply line L1 is positive with respect to supply line L2 (E16. 1), capacitor Ccharges sufficiently through primary winding PR of transformer TRS, diode D and biasing resistor R to trigger silicon controlled rectifier SCR to fire through its anode-cathode circuit. As rectifier SCR fires, a high inrush of current flows through primary winding PR. The fast rise time of the inrush of voltage, induces a voltage in secondary winding SEC of transformer TRS, which voltage is of insufficient magnitude to are across spark gap 80. However, this energy is stored in distributive capacitance in transformer secondary windings SEC.

As the transformer flux field starts to collapse, the distributive capacitance discharges through secondary winding SEC to produce voltage spikes of from 150 to 200 volts in primary winding PR of transformer TRS as shown in voltage waveform VP taken from an oscillograph. These voltage spikes lag the applied voltage by approximately 1.2 milliseconds and drive the anode electrode of silicon controlled rectifier SCR momentarily sufficiently negative with respect to its cathode to stop conduction of the rectifier.

The 150 to 200 voltage spike in primary winding PR is transformed by step-up spark transformer TRS at a 1 to turns ratio to provide an output voltage in secondary winding SEC of from 13,500 to 18,000 volts. This voltage arcs across gap SG to ignite gaseous fuel in the vicinity of the gap.

Since the anode electrode of silicon controlled rectifier SCR is momentarily driven negative to stop conduction for approximately only 800 microseconds after which it again becomes positive, rectifier SCR again fires. The abovedescribed sequence is, therefore, repeated, producing another output high voltage arc. Since with the 60 cycle supply, the positive half-cycle duration is 8.3 milliseconds, this provides seven output pulses of from 13,500 to 18,000 volts across spark gap SG for each positive half cycle of the voltage applied to lines L1, L2 with a starting delay of 1.2 milliseconds and a shutoff time near the end of the half cycle of 1.1 milliseconds. The transient pulses of from to 200 volts are of microseconds peak duration, with periods of nonconduction of rectifier SCR of 800 microseconds, as is indicated by voltage waveform VP and primary current waveform PC of FIG. 2.

During the negative half cycle of applied power AV, as may be seen from waveforms AV, VP and PC of FIG. 2, silicon controlled rectifier SCR is maintained in nonconducting condition due to its anode being at a negative potential. Therefore, no high voltage spark is produced during the 8.3 millisecond period of the negative half cycle' of the applied power.

It may be noted that with the subject arrangement one of the lowest cost silicon controlled rectifiers now available on the market may be utilized to provide the switching action. This inexpensive rectifier gives good operation, although the current and voltages through it momentarily far exceed its ratings. This is possible, since the transient pulses are of very short duration and the rectifier is allowed to recover within the comparatively long interval between pulses. Fast switching action of rectifier SCR to obtain the transients for transformation to high voltage sparks is obtained by biasing the gate of the rectifier through the anode circuit to assure that the gate electrode is never positive unless the anode is also positive. With the subject arrangement, high intensity sparking is obtained inexpensively for igniting gaseous fuel without the use of bulky transformers or special wiring arrangements.

As changes can be made in the above-described construction and many apparently different embodiments of this invention can be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown on the accompanying drawing be interpreted as illustrative only and not in a limiting sense.

lclaim:

11. A high voltage spark generator for providing a spark across a pair of electrodes forming a spark gap comprising:

a spark transformer having primary and secondary windings,

- a pair of spark electrodes spaced apart and connected across the secondary winding of said transfonner to provide a predetermined spark gap,

a silicon controlled rectifier having anode, gate and cathode electrodes,

said primary winding of said transformer being connected in the anode-cathode circuit of said rectifier for energization from a low voltage alternating power source,

characterized in that;

a blocking diode and biasing resistor are provided and 

1. A high voltage spark generator for providing a spark across a pair of electrodes forming a spark gap comprising: a spark transformer having primary and secondary windings, a pair of spark electrodes spaced apart and connected across the secondary winding of said transformer to provide a predetermined spark gap, a silicon controlled rectifier having anode, gate and cathode electrodes, said primary winding of said transformer being connected in the anode-cathode circuit of said rectifier for energization from a low voltage alternating power source, characterized in that; a blocking diode and biasing resistor are provided and connected in series to allow current flow from said anode electrode of said rectifier to its said gate electrode, and a firing capacitor is provided interconnected directly between said gate and cathode electrodes of said rectifier.
 2. The arrangement as set forth in claim 1 wherein said spark transformer has a ''''step-up'''' turns ratio of approximately 1 to
 90. 